This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-246232, filed Aug. 31, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a color image processing device adaptable to an image forming apparatus for forming the image of an object onto a transferred material.
In the field of color printing and color copying (including printouts by printers), a method has been widely used which forms color images by using black (K) in addition to three primary colors of cyan (C), magenta (M) and yellow (Y) (chromatic colors) in the subtractive primaries of color mixture. The reason why black is used is that color materials of C, M and Y can be saved, the reproducibility of shadow portions can be improved, and gray balance can be ensured easily (the density of black can be increased) in comparison with image forming by only three primary colors of C, M and Y. As color materials, inks are used in printing and part of printers and toners are used in color copying and most color printers.
In order to form color images using four colors, it is required to convert C, M and Y data (color data) into C, M, Y and K data (color data and black data), which is referred to as a black-coloring process.
As a black-coloring algorithm, xe2x80x9cLogical Algorithm of Black Ink Printingxe2x80x9d is disclosed by Shinji Kita in the fifth Chromatic Engineering Conference, p 59-62, 1988, according to which, even if a black-coloring signal is maximum, color signals can be reduced by black-coloring, and the amount of black is increased in achromatic-color high-density portions and the amount of black is increased as much as possible in chromatic color portions as well. This method is known as a GCR (Gray Component Replacement) method which permits good color reproduction using the average overlapping model for dots which overlap in the black-coloring process.
In the GCR method, however, there is a problem that the consumption of materials for chromatic colors increases because chromatic color materials are further used although the amount of black has already reached a maximum. In addition, there is another problem that color materials, toners in particular, may peel off paper when the total amount of all the color material of black, C, M, and Y exceeds a given amount.
On the other hand, C, M, Y and K signals resulting from the black-coloring process have advantages that black is reproduced deeply and the reproducibility of chromatic colors in high-density portions is not degraded by the use of too much black in those portions.
However, the superposition (or misalignment) of multiple color materials and the misalignment of black must be taken into consideration.
For example, if, when the amount of black is little in an achromatic high-density area adjacent to an area which is printed in black only (black area), the black area and the high-density area are displaced relative to each other, then not a black image but a white image will be produced. This is due to the fact that a difference in density is produced between the black area and the adjacent area because a color in the adjacent area which should originally have been represented by the superposition of colors is represented by black only.
An object of the present invention is to provide a color image processing device which is adapted for image forming apparatus and which has an increased degree of freedom in black-coloring processing based on the GCR system and permits color images which have good color reproducibility and are less susceptible to position displacement in black-colored portions to be output without affecting image processing on portions other than black-coloring portions and peeling of color materials.
The present invention provides a color image forming apparatus comprising: black-coloring processing portion for decomposing first color image signals each corresponding to one of multiple colors into second color signals and a black signal, and output section for outputting the second color signals and the black signal as a color image using chromatic color materials and a black color material, and wherein the black-coloring processing portion decomposes the first color signals into the second color signals and the black signal in accordance with
K=f(min(I))
A=h(I)xe2x88x92j(g(min(I)))
B=i(I)xe2x88x92k(g(min(I)))
Ixe2x80x2=A÷B (Axe2x89xa0B or Bxe2x89xa00)
where K is the black signal, I is the first color signals, Ixe2x80x2 is the second color signals, min(I) is the minimum among the first color signals, f(min(I)) is a function of min(I), g(min(I)) is a function of min(I), h(I) is a function of I, i(I) is a function of I, j(g(min(I))) is a function of g(min(I)), and k(g(min(I))) is a function of g(min(I)).
In addition, the present invention provides a color image forming apparatus comprising: first range correction section for compressing the signal range of first color image signals each corresponding one of multiple colors to produce second color signals; black-coloring processing portion for decomposing the second color image signals from the first range correction section into third color signals and a black signal; second range correction section for expanding the signal range of the third color signals and the black signal; and output section for outputting the color signals and the black signal from the second range correction section as a color image, and wherein the black-coloring processing portion decomposes the first color signals into the second color signals and the black signal in accordance with
K=f(min(I))
A=Ixe2x88x92g(min(I))
B=Ixe2x88x92g(min(I))
Ixe2x80x2=A÷B (Axe2x89xa0B or Bxe2x89xa00)
where K is the black signal, I is the second color signals, Ixe2x80x2 is the third color signals, min(I) is the minimum among the second color signals, f(min(I)) is a function of min(I), g(min(I)) is a function of min(I), h(I) is a function of I, i(I) is a function of I, j(g(min(I))) is a function of g(min(I)), and k(g(min(I))) is a function of g(min(I)).
Moreover, the present invention provides a color image forming apparatus comprising: color signal switching section for, at normal operation time, selectively outputting signals supplied directly or indirectly from color conversion section and, at color conversion table creation time, selectively outputting arbitrarily set signals to black-coloring processing portion; output section for outputting color signals and a black signal decomposed by the black-coloring processing portion as a color image; color data extraction section for extracting color data from image data outputted by the output section; and color conversion information creation section for creating To information representing a transformat ion relationship from a color coordinate system before the color conversion to a color coordinate system after the color conversion on the basis of the correspondence between the extracted color data and the arbitrarily set signals, and wherein the black-coloring processing portion decomposes the first color signals into the second color signals and a black signal in accordance with
K=xcex1xc3x97(min(I))
A=g(I)xe2x88x92h(k2)
B=i(I)xe2x88x92j(k2)
Ixe2x80x2=A÷B (Axe2x89xa0B or Bxe2x89xa00)
where K is the black signal, I is the first color signals, Ixe2x80x2 is the second color signals, min(I) is the minimum among the first color signals, xcex1 is f(min(I) or a constant, k2 is the amount by which underlying color is removed (less than min(I)), g(min(I)) is a function of min(I), h(k2) is a function of k2, i(I) is a function of I, and j(k2) is a function of k2.
Furthermore, the present invention provides a color image forming apparatus comprising: color signal switching section for, at normal operation time, selectively outputting signals supplied directly or indirectly from color conversion section and, at color conversion table creation time, selectively outputting arbitrarily set signals to first range correction section for compressing the signal range of input signals; black-coloring processing portion for performing a black-coloring process on the signals corrected by the first range correction section; second range correction section for expanding the signal range of the signals subjected to the black-coloring process by the black-coloring processing portion; color data extraction section for extracting color data from image data outputted by the output section; and color conversion information creation section for creating information representing a transformation relationship from a color coordinate system before the color conversion to a color coordinate system after the color conversion on the basis of the correspondence between the extracted color data and the arbitrarily set signals, and wherein the black-coloring processing portion decomposes the first color signals into the second color signals and the black signal in accordance with
K=f(min(I))
A=Ixe2x88x92g(min(I))
B=Ixe2x88x92g(min(I))
Ixe2x80x2=A÷B (Axe2x89xa0B or Bxe2x89xa00)
where K is the black signal, I is the second color signals, Ixe2x80x2 is the third color signals, min(I) is the minimum among the second color signals, f(min(I)) is a function of min(I), g(min(I)) is a function of min(I), h(I) is a function of I, i(I) is a function of I, j(g(min(I))) is a function of g(min(I)), and k(g(min(I))) is a function of g(min(I)).
Further, the present invention provides a color image forming apparatus comprising: black-coloring processing portion for decomposing first color image signals each corresponding to one of multiple colors into second color signals and a black signal; extraction section for extracting an image area to be output in black only in the color signals; black conversion section for converting color image signals for the image area to be output in black only into black signals; and output section for outputting a color image corresponding to the second color signals and the black signals from the black conversion section, and wherein the black-coloring processing portion decomposes the first color image signals into the second color signals and the black signal so that the black signal is increased preferentially in achromatic high-density image portions, the color signals are increased in other image portions, and the total of the amounts of color materials and the amount of black material used in the output section is not larger than a predetermined value.
In addition, the present invention provides a color image forming apparatus comprising: color signal switching section for, at normal operation time, selectively outputting signals supplied directly or indirectly from color conversion section and, at color conversion table creation time, selectively outputting arbitrarily set signals to black-coloring processing portion; extraction section for extracting an image area to be output in black only in the color signals; black conversion section for converting color image signals for the image area to be output in black only extracted by the extraction section into black signals; output section for outputting color signals and a black signal decomposed by the black-coloring processing portion as a color image; color data extraction section for extracting color data from image data outputted by the output section; and color conversion information creation section for creating information representing a transformation relationship from a color coordinate system before the color conversion to a color coordinate system after the color conversion on the basis of the correspondence between the extracted color data and the arbitrarily set signals, and wherein the black-coloring processing portion decomposes the first color image signals into the second color signals and the black signal so that the black signal is increased preferentially in achromatic high-density image portions, the color signals are increased in other image portions, and the total of the amounts of color materials and the amount of black material used in the output section is not larger than a predetermined value.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.